It is well known to include in various kinds of imaging elements, a transparent layer containing magnetic particles dispersed in a polymeric binder. The inclusion and use of such transparent magnetic recording layers in light-sensitive silver halide photographic elements has been described in U.S. Pat. Nos. 3,782,947; 4,279,945; 4,302,523; 5,217,804; 5,229,259; 5,395,743; 5,413,900; 5,427,900; 5,498,512; and others. Such elements are advantageous because images can be recorded by customary photographic processes while information can be recorded simultaneously into or read from the magnetic recording layer by techniques similar to those employed for traditional magnetic recording art.
A difficulty, however, arises in that magnetic recording layers generally employed by the magnetic recording industry are opaque, not only because of the nature of the magnetic particles, but also because of the requirements that these layers contain other addenda which further influence the optical properties of the layer. Also, the requirements for recording and reading of the magnetic signal from a transparent magnetic layer are more stringent than for conventional magnetic recording media because of the extremely low coverage of magnetic particles required to ensure transparency of the transparent magnetic layer as well as the fundamental nature of the photographic element itself. Further, the presence of the magnetic recording layer cannot interfere with the function of the photographic imaging element.
The transparent magnetic recording layer must be capable of accurate recording and playback of digitally encoded information repeatedly on demand by various devices such as a camera or a photofinishing or printing apparatus. The layer also must exhibit excellent running, durability (i.e., abrasion and scratch resistance), and magnetic head-cleaning properties without adversely affecting the imaging quality of the photographic elements. However, this goal is extremely difficult to achieve because of the nature and concentration of the magnetic particles required to provide sufficient signal to write and read magnetically stored data and the effect of any noticeable color, haze or grain associated with the magnetic layer on the optical density and granularity of the photographic elements. These goals are particularly difficult to achieve when magnetically recorded information is stored and read from the photographic image area. Further, because of the curl of the photographic element, primarily due to the photographic layers and the core set of the support, the magnetic layer must be held more tightly against the magnetic heads than in conventional magnetic recording in order to maintain planarity at the head-media interface during recording and playback operations. Thus, all of these various characteristics must be considered both independently and cumulatively in order to arrive at a commercially viable photographic element containing a transparent magnetic recording layer that will not have a detrimental effect on the photographic imaging performance and still withstand repeated and numerous read-write operations by a magnetic head.
Problems associated with the generation and discharge of electrostatic charge during the manufacture and use of photographic film and paper have been recognized for many years by the photographic industry. The accumulation of charge on film or paper surfaces leads to the attraction of dust, which can produce physical defects. The discharge of accumulated charge during or after the application of the sensitized emulsion layers can produce irregular fog patterns or static marks in the emulsion. The severity of the static problems has been exacerbated greatly by the increases in sensitivity of new emulsions, increases in coating machine speeds, and increases in post-coating drying efficiency. The charge generated during the coating process results primarily from the tendency of webs of high dielectric constant polymeric film base to undergo triboelectric charging during winding and unwinding operations, during conveyance through the coating machines, and during post-coating operations such as slitting, perforating, and spooling. Static charge can also be generated during the use of the finished photographic product. For example, in an automatic camera, because of the repeated motion of the photographic film in and out of the film cassette, there is the added problem of the generation of electrostatic charge by the movement of the film across the magnetic heads and by the repeated winding and unwinding operations, especially in a low relative humidity environment. The accumulation of charge on the film surface results in the attraction and adhesion of dust to the film. The presence of dust not only can result in the introduction of physical defects and the degradation of the image quality of the photographic element but also can result in the introduction of noise and the degradation of magnetic recording performance (e.g., S/N ratio, "drop-outs", etc.). This degradation of magnetic recording performance can arise from various sources including signal loss resulting from increased head-media spacing, electrical noise caused by discharge of the static charge by the magnetic head during playback, uneven film transport across the magnetic heads, clogging of the magnetic head gap, and excessive wear of the magnetic heads. In order to prevent these problems arising from electrostatic charging, there are various well known methods by which an electrically-conductive layer can be introduced into the photographic element to dissipate any accumulated electrostatic charge.
Antistatic layers containing electrically-conductive agents can be applied to one or both sides of the film base as subbing layers either beneath or on the side opposite to the silver halide emulsion layers. An antistatic layer also can be applied as an outer layer coated either over the emulsion layers or on the side opposite to the emulsion layers or on both sides of the film base. For some applications, it may be advantageous to incorporate the antistatic agent directly into the film base or to introduce it into a silver halide emulsion layer. Typically, in photographic elements of prior art comprising a transparent magnetic recording layer, the antistatic layer was preferably present as a backing layer underlying the magnetic recording layer.
The use of such electrically-conductive layers containing suitable semi-conductive metal oxide particles dispersed in a film-forming binder in combination with a transparent magnetic recording layer in silver halide imaging elements has been described in the following examples of the prior art. Photographic elements including a transparent magnetic recording layer and a transparent electrically-conductive layer both located on the backside of the film base have been described in U.S. Pat. Nos. 5,147,768; 5,229,259; 5,294,525; 5,336,589; 5,382,494; 5,413,900; 5,457,013; 5,459,021; and others. The conductive layers described in these patents contain fine granular particles of a semi-conductive crystalline metal oxide such as zinc oxide, titania, tin oxide, alumina, indium oxide, silica, complex or compound oxides thereof, and zinc antimonate or indium antimonate dispersed in a polymeric film-forming binder. Of these conductive metal oxides, antimony-doped tin oxide and zinc antimonate are preferred. A granular, antimony-doped tin oxide particle commercially available from Ishihara Sangyo Kaisha under the tradename "SN-100P" was disclosed as particularly preferred in Japanese Kokai Nos. 04-062543, 06-161033, and 07-168293.
The preferred average diameter for granular conductive metal oxide particles was disclosed as less than 0.5 .mu.m in U.S. Pat. No. 5,294,525; 0.02 to 0.5 .mu.m in U.S. Pat. No. 5,382,494; 0.01 to 0.1 .mu.m in U.S. Pat. Nos. 5,459,021 and 5,457,013; and 0.01 to 0.05 .mu.m in U.S. Pat. No. 5,457,013. Suitable conductive metal oxide particles exhibit specific volume resistivities of 1.times.10.sup.10 ohm.cm or less, preferably 1.times.10.sup.7 ohm.cm or less, and more preferably 1.times.10.sup.5 ohm.cm or less as taught in U.S. Pat. No. 5,459,021. Another physical property used to characterize crystalline metal oxide particles is the average x-ray crystallite size. The concept of crystallite size is described in detail in U.S. Pat. No. 5,484,694 and references cited therein. Transparent conductive layers containing semiconductive antimony-doped tin oxide granular particles exhibiting a preferred crystallite size of less than 10 nm are taught in U.S. Pat. No. 5,484,694 to be particularly useful in imaging elements. Similarly, photographic elements comprising transparent magnetic layers in combination with conductive layers containing granular conductive metal oxide particle with average crystallite sizes ranging from 1 to 20 nm, preferably 1 to 5 nm, and more preferably from 1 to 3.5 nm are claimed in U.S. Pat. No. 5,459,021. Advantages to using metal oxide particles with small crystallite sizes are disclosed in U.S. Pat. Nos. 5,484,694 and 5,459,021 including the ability to be milled to a very small size without significant degradation of electrical performance, ability to produce a specified level of conductivity at lower weight loadings and/or dry coverages, as well as decreased optical density, decreased brittleness, and decreased cracking of conductive layers containing such particles.
Conductive layers containing such metal oxide particles have been applied at the following preferred ranges of dry weight coverages of metal oxide: 3.5 to 10 g/m.sup.2 ; 0.1 to 10 g/m.sup.2 ; 0.002 to 1 g/m.sup.2 ; 0.05 to 0.4 g/m.sup.2 as disclosed in U.S. Pat. Nos. 5,382,494; 5,457,013; 5,459,021; and 5,294,525, respectively. Preferred ranges for the metal oxide fraction in the conductive layer include: 17 to 67 weight percent, 43 to 87.5 weight percent, and 30 to 40 volume percent as disclosed in U.S. Pat. Nos. 5,294,525; 5,382,494; and 5,459,021, respectively. Surface electrical resistivity (SER) values were reported in U.S. Pat. No. 5,382,494 for conductive layers measured prior to overcoating with a transparent magnetic layer as ranging from 10.sup.5 to 10.sup.7 ohm/square and from 10.sup.6 to 10.sup.8 ohm/square after overcoating. Surface resistivity values of about 10.sup.8 to 10.sup.11 ohm/square for conductive layers overcoated with a transparent magnetic layer were reported in U.S. Pat. Nos. 5,457,013 and 5,459,021.
In addition to the antistatic layer being present as a backing or subbing layer, the inclusion of conductive tin oxide granular particles with an average diameter less than 0.15 .mu.m in a transparent magnetic recording layer with cellulose acetate binder is disclosed in U.S. Pat. Nos. 5,147,768; 5,427,900 and Japanese Kokai No. 07-159912. For a tin oxide fraction of about 92 weight percent, the surface resistivity of the conductive layer is reported to be approximately 1.times.10.sup.11 ohm/square in U.S. Pat. No. 5,427,900.
Photographic elements including an electrically-conductive layer containing colloidal "amorphous" silver-doped vanadium pentoxide and a transparent magnetic recording layer have been disclosed in U.S. Pat. Nos. 5,395,743; 5,427,900; 5,432,050; 5,498,512; 5,514,528 and others. Colloidal vanadium oxide is composed of entangled conductive microscopic fibrils or ribbons that are 0.005-0.01 .mu.m wide, about 0.001 .mu.m thick, and 0.1-1 .mu.m in length. Conductive layers containing colloidal vanadium pentoxide prepared as described in U.S. Pat. No. 4,203,769 can exhibit low surface resistivities at very low weight fractions and dry weight coverages of vanadium oxide, low optical losses, and excellent adhesion of the conductive layer to film supports. However, colloidal vanadium pentoxide readily dissolves at high pH in developer solution during wet processing and must be protected by a nonpermeable, overlying barrier layer. Examples of suitable barrier layers are taught in U.S. Pat. Nos. 5,006,451; 5,284,714; and 5,366,855. Further, when a conductive layer containing colloidal vanadium pentoxide underlies a transparent magnetic layer, the magnetic layer inherently can serve as a nonpermeable barrier layer. However, if the magnetic layer contains a high level of reinforcing filler particles, such as gamma aluminum oxide or silica fine particles, it must be crosslinked using suitable cross-linking agents in order to preserve the desired barrier properties, as taught in U.S. Pat. No. 5,432,050.
Alternatively, a film-forming sulfopolyester latex or polyesterionomer binder can be combined with the colloidal vanadium pentoxide in the conductive layer to minimize degradation during processing as taught in U.S. Pat. Nos. 5,360,706; 5,380,584; 5,427,835; 5,576,163; and others. Furthermore, it is disclosed that the use of a polyesterionomer can improve solution stability of colloidal vanadium pentoxide containing dispersions. Instability of vanadium pentoxide gels in the presence of various binders is well known and several specific classes of polymeric binders have been identified for improved stability or coatability, for example in U.S. Pat. Nos. 5,427,835; 5,439,785; 5,360,706; and 5,709,984. U.S. Pat. No. 5,427,835 teaches the use of sulfopolymers in combinations with vanadium oxide preferably prepared from hydrolysis of oxoalkoxides for antistatic applications. A specific advantage cited for preparation of vanadium oxide gels from oxoalkoxides is the ability to control the vanadium oxidation state. Colloidal vanadium oxide gels are described as viscous dark brown solutions which become homogeneous upon aging. Comparative Example 3 describes the formation of "dark greenish clots" upon mixing with polyacrylic acid indicating a change in oxidation state and flocculation of the gel. Similarly, the examples of sulfopolymers with vanadium oxide result in a color change from dark brown to dark greenish-brown, again indicating a potentially undesirable change in vanadium oxidation state. Sulfopolymers indicated to be useful include sulfopolyester, ethylenically-unsaturated sulfolpolymers, sulfopolyurethanes, sulfopolyurethane/-polyureas, sulfopolyester polyols, sulfopolyols, sulfonate containing polymers such as poly(sodiumstyrene sulfonate) and alkylene oxide-co-sulfonate containing polyesters. However, as indicated hereinbelow by comparative examples, not all of the above sulfopolymers provide adequate adhesion when overcoated with a transparent magnetic recording layer.
U.S. Pat. No. 5,439,785 teaches the use of a specified ratio of sulfopolymer to vanadium oxide to provide an antistatic formulation which remains conductive after photographic processing. A range of from 1:20 to 1:150 V.sub.2 O.sub.5 :sulfopolymer is specified. Surface electrical resistivity values are typically greater than 1.times.10.sup.9 ohm/square for the indicated range. At lower colloidal vanadium oxide levels, the conductivity is insufficient to provide antistatic protection; at higher vanadium oxide levels the antistatic layer loses conductivity when subjected to photographic processing. However, prior art colloidal vanadium pentoxide typically have significantly lower resistivity values, i.e., 1.times.10.sup.8 ohm/square. Consequently, one of the primary benefits of colloidal vanadium oxide, low resistivity at low dry weight coverage is not achieved.
Colloidal vanadium oxide dispersed with a terpolymer of vinylidene chloride, acrylonitrile, and acrylic acid coated on subbed polyester supports and overcoated with a transparent magnetic recording layer is taught in U.S. Pat. Nos. 5,432,050 and 5,514,528. U.S. Pat. No. 5,514,528 also teaches an antistatic layer consisting of colloidal vanadium oxide and an aqueous dispersible polyester coated on a subbed polyester support and subsequently overcoated with a transparent magnetic recording layer.
U.S. Pat. No. 5,718,995 teaches an antistatic layer containing an electrically-conductive agent and a specified polyurethane binder having excellent adhesion to surface treated or subbed polyester supports and to an overlying transparent magnetic layer. The specified polyurethane is an aliphatic, anionic polyurethane having an ultimate elongation to break of at least 350 percent, however, sulfonated polyurethanes are neither taught nor claimed. Comparative Example 1 of '995 demonstrates that it is difficult to achieve adequate adhesion to glow discharge treated polyethylene naphthalate for a magnetics backing package consisting of a solvent coated cellulosic-based magnetic layer and an antistatic layer containing colloidal vanadium pentoxide and either a sulfopolyester or interpolymer of vinylidene chloride cited as preferred binders in the above mentioned U.S. patents. It was further demonstrated in Comparative Examples 9-13 that electrically-conductive layers composed of a non-preferred polyurethane binder also did not provide adequate adhesion. Electrically-conductive agents taught for use in combination with the specified polyurethane binder included tin oxide, colloidal vanadium oxide, zinc antimonate, indium antimonate and carbon fibers. It was further disclosed that electrically-conductive polymers as exemplified by polyanilines and polythiophenes may also be used. However, it was indicated that a coating composition consisting of the specified polyurethane binder and colloidal vanadium oxide had limited shelf-life (less then 48 hrs). As indicated by Comparative Examples of the present invention, solution stability is also unacceptable for a coating composition consisting of an electrically-conductive polypyrrole and Witcobond W-236 (commercially available from Witco Corporation) a preferred polyurethane disclosed in '995. Comparative Examples shown herein demonstrate unacceptable solution stability for electrically-conductive layers containing a non-sulfonated polyurethane binder and either polypyrrole or colloidal vanadium oxide.
U.S. Pat. No. 5,726,001 teaches an adhesion promoting polyurethane layer coated either above or below an electrically-conductive layer which can improve adhesion for an overlying transparent magnetic recording layer. Without, the addition of the adhesion promoting layer, a magnetic backing package containing an electrically-conductive layer consisting of an anionic aliphatic polyurethane having an ultimate elongation to break of at least 350 percent and colloidal vanadium oxide at either a 1/1 or 4/1 weight ratio was demonstrated to have unacceptable adhesion. Consequently, an increase in the binder/vanadium oxide ratio is required which typically results in reduced conductivity and solution stability. The use of an additional layer for improved adhesion is undesirable due to increased coating complexity.
The use of crystalline, single-phase, acicular, conductive metal-containing particles in transparent conductive layers for various types of imaging elements also containing a transparent magnetic recording layer has been disclosed in U.S. Pat. No. 5,731,119 incorporated herein by reference with regards to suitable acicular particles for use in various imaging elements containing a transparent magnetic recording layer. Suitable acicular, conductive metal-containing particles have a cross-sectional diameter .ltoreq.0.02 .mu.m and an aspect ratio (length to cross-sectional diameter) .gtoreq.5:1. Preferred acicular, conductive metal-containing particles have an aspect ratio .gtoreq.10:1.
Electrically-conducting polymers have recently received attention from various industries because of their electronic conductivity. Although many of these polymers are highly colored and are less suited for photographic applications, some of these electrically conducting polymers, such as substituted or unsubstituted pyrrole-containing polymers (as disclosed in U.S. Pat. Nos. 5,665,498 and 5,674,654), substituted or unsubstituted thiophene-containing polymers (as disclosed in U.S. Pat. Nos. 5,300,575; 5,312,681; 5,354,613; 5,370,981; 5,372,924; 5,391,472; 5,403,467; 5,443,944; 5,575,898; 4,987,042 and 4,731,408) and substituted or unsubstituted aniline-containing polymers (as disclosed in U.S. Pat. Nos. 5,716,550; 5,093,439 and 4,070,189) are transparent and not prohibitively colored, at least when coated in thin layers at moderate coverage. Because of their electronic conductivity instead of ionic conductivity, these polymers are conducting even at low humidity. Moreover, these polymers can retain sufficient conductivity even after wet chemical processing to provide what is known in the art as "process-surviving" antistatic characteristics to the photographic support they are applied to.
The use of electronically-conductive polythiophenes in an electrically-conductive layer either below or above a transparent magnetic layer is taught is U.S. Pat. No. 5,443,944. Suitable polythiophenes are prepared by oxidative polymerization of thiophene in the presence of polymeric carboxylic acids or polymeric sulfonic acids. Examples of polythiophene-containing antistatic layers either had no polymeric film-forming binder, a vinylidene chloride based terpolymer, or a polyurethane. The polyurethane binder was indicated to give "insufficient antistatic effects."
An electrically-conductive layer containing poly(3,4-ethylene dioxypyrrole/styrene sulfonate) in a film-forming binder used in combination with a transparent magnetic layer is claimed in U.S. Pat. No. 5,665,498. Similarly, an electrically-conductive layer containing polypyrrole/poly(styrene sulfonic acid) used in combination with a transparent magnetic layer is disclosed in U.S. Pat. No. 5,674,654. Suitable film-forming binders are indicated to include aqueous dispersions of polyurethanes or polyesterionomers. However, neither polyurethane film-forming binders nor a transparent recording layer overlying the electrically-conductive layer are taught. Sulfonated polyester binders as taught in '498 and '654 have resulted in insufficient adhesion to an overlying magnetic layer.
U.S. Pat. No. 5,707,791 claims a silver halide element having a resin layer consisting of an antistatic agent and an aqueous-dispersible polyester resin or an aqueous-dispersible polyurethane resin, and magnetic layer coated on the resin layer. The antistatic agent is selected from the group consisting of a conductive polymer and a metal oxide. Suitable methods of making the polyurethane water dispersible are disclosed to include introducing a carboxyl group, sulfon group or tertiatry amino group into the polyurethane. Furthermore, the conductive polymers indicated are preferably anionic or cationic ionically-conducting polymers. Electronically-conducting polymers such as polythiophenes, polyanilines, or polypyrroles are not indicated.
U.S. Pat. No. 5,382,494 claims a silver halide photographic material having a magnetic recording layer on a backing layer. The backing layer contains inorganic particles of a metal oxide which have at least one surface being water-insoluble, and dispersed in a binder in a proportion of 75.0% to 660% by weight of the binder. Suitable binders include a polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane resin and a polyester resin. It is further disclosed that "the backing layer is allowed to contain an organic particles in place of the inorganic particles."
U.S. Pat. No. 5,294,525 discloses a silver halide photographic material containing a transparent magnetic layer, a conductive layer containing conductive particles and a binder. The binder contains a polar functional group consisting of --SO.sub.2 M, --OSO.sub.3 M and --P(.dbd.O)(OM.sub.1)(OM.sub.2) wherein M is hydrogen, sodium, potassium, or lithium; M.sub.1 and M.sub.2 are the same or different and represent hydrogen, sodium, potassium, lithium, or an alkyl group. Suitable binder resins include polyvinyl chloride resins, polyurethane resins, polyester resins and polyethylene type resins. However, '525 additionally requires the binder for the magnetic layer contain a polar functional group indicated above. The required addition of a polar functional group in the binder of the magnetic layer is undesirable for the physical and chemical properties of the magnetic layer. Furthermore, increased permeability of the magnetic binder can potentially result in chemical change of the magnetic particles and consequently alter the desired magnetic signal.
Because the requirements for an electrically-conductive layer to be useful in an imaging element are extremely demanding, the art has long sought to develop improved conductive layers exhibiting a balance of the necessary chemical, physical, optical, and electrical properties. As indicated hereinabove, the prior art for providing electrically-conductive layers useful for imaging elements is extensive and a wide variety of suitable electroconductive materials have been disclosed. However, there is still a critical need in the art for improved conductive layers which can be used in a wide variety of imaging elements, which can be manufactured at a reasonable cost, which are resistant to the effects of humidity change, which are durable and abrasion-resistant, which do not exhibit adverse sensitometric or photographic effects, which exhibit acceptable adhesion to overlying or underlying layers, which exhibit suitable cohesion, and which are substantially insoluble in solutions with which the imaging element comes in contact, such as processing solutions used for photographic elements. Further, to provide both effective magnetic recording properties and effective electrical-conductivity for an imaging element, without impairing its imaging characteristics, poses a considerably greater technical challenge.
It is toward the objective of providing a useful combination of a transparent magnetic recording layer and an electrically-conductive layer which can be comprised of a wide variety of electrically-conductive agents and have acceptable adhesion to underlying and overlying layers that more effectively meet the diverse needs of imaging elements, especially those of silver halide photographic films, but also of a wide variety of other types of imaging elements than those of the prior art that the present invention is directed.